1. Field of the Invention
The present invention relates to an endoscope insertion portion of an endoscope having a plurality of observation optical systems.
2. Description of the Related Art
Conventionally, endoscopes have been widely used in the medical field and the like. With an endoscope, for example, internal organs in a body cavity can be observed by inserting an elongated insertion portion into the body cavity, and various treatments can be performed using a treatment instrument inserted into a treatment instrument insertion channel as necessary. At a distal end of the insertion portion, a bending portion is provided. By operating an operation portion of the endoscope, observing direction of an observation window at a distal end portion can be changed.
In general, an endoscope is provided with an air/water feeding nozzle for cleaning for a case where body fluid or the like adheres on an outer surface of the objective optical system of the endoscope to disturb the observation when the endoscope is inserted into the body cavity. The outer surface of the objective optical system of the endoscope can be secured of a clean observation field of view with, for example, a cleaning liquid spouted out or air sprayed from the air/water feeding nozzle.
Further, an endoscope is used to observe the inside of the body cavity where little natural light enters. Therefore, in an endoscope, to obtain photographing light to be taken in from an observation window, illumination light led by a light guide or the like is irradiated into the body cavity from an illumination window.
For example, an endoscope having a plurality of objective optical systems is proposed as described in Japanese unexamined patent publication No. 06-154155. This endoscope has a plurality of image pickup units, wherein the plurality of objective optical systems and an aperture of an air/water feeding nozzle are located at a distal end of an insertion portion to line up on a generally straight line.
As mentioned above, it is desirable for an endoscope to have a large observation window, that is, to increase lens diameter of the object optical system, in order to obtain enough photographing light level by illumination light from an illumination window in the body cavity where little natural light enters, so that fine observation can be performed.